This invention relates to a rotary tool for machining multiple surfaces in a stationary workpiece. The invention is especially suited to the machining of multiple surfaces in an intake or exhaust passage in an engine cylinder head. A principal aim of the invention is to achieve multiple machining operations on a valve passage in a single pass of the machine tool.
In one conventional engine the cylinder head has multiple passages for delivering air to the combustion chambers, or for exhausting combustion products out of the combustion chambers. Each passage has a poppet valve therein for controlling gaseous flow. Each poppet valve has a peripheral edge surface seatable against an annular valve seat formed near the mouths of the passage.
Typically each valve seat is angled to the passage axis at forty five degrees. The mouth of the passage in direct connection with the valve seat is angled to the passage axis at sixty degrees. The face of the cylinder head bordering the mouth surface has a relatively slight angulation to the cylinder head surface. The annular throat surface leading to, or from, the valve seat is angled to the passage axis at fifteen degrees.
The angulation on the various passage surfaces facilitates a relatively smooth gaseous flow between the combustion chamber and the associated intake or exhaust passage. To achieve a relatively smooth surface finish, each of the described passage surfaces is machined to the desired angulation. The machining operations on the four described surfaces can be time-consuming when performed separately by separate machine tools.
The present invention relates to a machine tool for simultaneously machining multiple surfaces on a stationary workpiece during a single pass of the tool, thereby reducing the total time required to machine the various surfaces. The invention is particularly suited to the machining of multiple surfaces on the passages of an engine cylinder head.
A machine tool embodying the invention will typically be a vertical end milling machine that includes a rotary tool body mounted for simultaneous rotation and axial motion downward toward the mouth of a passage formed in a stationary cylinder head. The tool body has four cutter assemblies equidistantly spaced around the tool body circumference. Each cutter assembly includes a mounting mechanism and a cutting element adjustably positioned on the mounting mechanism, so that the cutting edges on the cutting elements can have precise positionment relative to passage surfaces on the workpiece (cylinder head). At least some of the cutting elements have two cutting edges angled at different angles to the tool body rotational axis.
The cutting elements are oriented so that during each revolution of the tool body each cutting edge on each cutting element exerts a predetermined cutting action on an aligned workpiece surface. A complete machining operation on multiple workpiece surfaces is achieved in a single downward plunge of the tool body. The total body stroke can be controlled as a function of time.
Specific features of the invention will be apparent from the attached drawings and description of a particular structural arrangement embodying the invention.